Piezo electric crystal system



Mzmh 14, 1933. A. cRossLEY y 1,901,735?.

PIEZOELECTRIG CRYSTAL SYSTEM Filed July 15, 1925 SH01 1 uut ?aten ted ar. 14, 1933 ALFRED CROSSLEY, V0F WASHINGTON, DISTRICT 0F COLUMBIA, ASSIGNOR, BY HESNE ASSIGNMENTS, T0 WIRED RADIO, TNC., 0F NEW YORK, N. Y., A CORPORATION OF DELAWARE PIEZO ELECTRIC CRYSTAL SYSTEM Application led July 15,

My inventionV relates broadly to control `devices for electron tube transmitters and Still another object ot my invention is to provide means for eliminatingl the detrimental eects of moisture from the surface of the crystals which I have found tends to impair the oscillation generating eticiency of 'the crystals.

A further object of my invention is to provide a mounting for piezo electric crystals whereby the crystals may operate at a certain temperature 4or range of temperature which permits maximum output with zero or minimum `frequency change.

Broadly, the object of this'invention is to provide means for mounting the piezo electric crystal in-a container which is so constructed that the interior of this container is maintained at a selected temperature which will permit maximum output with minimum frequency change, said temperature regulating system being effective in preventing the condensation of water or any other substance on the surface of the crystal.

'With the adaptationv of piezo electric uartz crystals to electron tube circuits in t e control of'electron tube transmitters and amplifiers, l vlinl that it is necessary to carefully protect the quartz crystals against moisture and change in temperature, if the oscillations generatedfbythe crystal are to be maintained constant.

llt has been observed that maximum oscillation generation output can be obtained from 1925. Serial No. 43,861.'

a crystal when the surfaces of the crystal are free from dirt or water. It is therefore customary to wash the crystal in alcohol to erase all traces of foreign substances from the surfaces and in some cases it is also necessary to heat the crystal to thoroughly dry the surface thereof. After this operation' the crystal is placed between the two contact plates and operated under best conditions. Should, however, during operation, the crystal become subjected to the condensation of foreign matter on its surfaces, the output eciency of the crystal will be impaired and if this condensation is excessive, the crystal will cease oscillating. l lt has been found that a very small drop of water placed on the surface of the crystal is sulicient to render a crystal inoperative.

l have also determined that a variation in thenatural oscillation frequency of the crystal occurs with a change in temperature of the crystal. It therefore is necessary to keep the crystal at one temperaturevor a narrow range of temperatures in order to obtain a constant frequency from the crystal. An-

other and important feature which enters intovr the eilicient operation of the crystal is the use of the proper 'area and. Weight of the upper contact plate. lt is necessaryto determine by experiment the proper area and weight of the upper contact plates. A plate of the same area as the upper surface of the crystal has been found satisfactory, but the weight of this plate is dependent on the natural frequency of the crystal. My 'experiments show that t e weight of the plate can be increased. with an increase in the natural frequency -of the crystal. The desired weight may be obtained by employing plates of the correct weight or it can be obtained by employing a thin plate with suitable spring pressing upon this plate.

ln order to maintain the crystal at its proper operating eiciency l employ a crystal container wherein a plurality of crystals may be.

maintained under a selected pressure and subjected to a constant temperature or range of temperature. The container is/hermetically sealed to avoid exposure of the lcrystals to the atmosphere and to humidity changes.

Switching means are provided on the container for selecting a. desired crystal out of the plurality of crystals for operation in a given control circuit.

My invention` will be more clearly understood from the following specification, by reference to the accompanying drawing, in which: i

Figure 1 is a perspective view of the crystal container partially broken away to show the interior arrangement of the crystals and temperature regulating mechanism within the container; Fig. 2 shows the electrical arrangement of the circuits within the crystal container; Fig. 3 is a plan view showing the arrangement of the crystals within the crystal container; Fig. 4; is a fragmentary view partially in cross section showing one of the pressure determining elements used in the crystal mounting; and Fig. 5 is a fragmentary view showing the method of making electrical connection with the crystal between the lower conductive surface of the crystal container and the upper contact plate.

Referring to the drawing in detail, reference character 1 indicates the crystal container which is hermetically sealed by a cover portion 2. rIhe container case may be constructed of any suitable material but is -preferably made of brass or aluminum. The bottom section 3 forms a metallic supporting surface upon which a suitable number of crystals indicated by `20, 2l and 22 are supported. This bottom plate 3i`has its surface machined 'f smooth and Hat so that the entire lower surface of the crystals 20, 21 and 22 make perfect contact with the bottom plate 3. The front of the crystal container includes a switchingv system comprising rotatable switch arm 8 an v cooperating .contacts 5, 6 and 7 which connect through leads 9, 10, and 1l with the spring members 15 under, which the crystals are maintainedat desired pressure. The spring members 15 bear upon contact plate members 16 which are positioned in contact with the upper surface of`crysta1s 20, 21 vand 22. Fig.

' 4 shows one method of maintaining tension upon spring members 15. An insulation block 14 is provided secured to the metallic surface 3 by screw members 13. A- binding post 12 is supported on the insulated block member 14`and holds spring member 15 with respect'thereto. To prevent the crystal from rsliding out from between upper contact plates 16 and the lower contact plate 3, means can be employed either inthe form of small metal or bakelite pegs 17 which surround the-crystals, as shown, or the metal under the crystal can be out away or recessed to house the lower sideV of vthe crystal. The upper Contact plate 16 is shown only as a plate with a connecting wire in Fig. 5, Whereas it may be aplate with la spiral or fiat spring 15 as shown in Fig-f4l pressing against it, or'-l any other means, whereby the best pressurecan be substituted for any deficiency in the weight of themetal plate that may be employed. The lower surfaces of the crystals 20, 21 and 22 are maintained in ,position with respect to ythe lower plate 3 by means of upwardly extending pegs 18 positioned at points around the periphery of the crystal. The provision of the peg members forms sockets in which the crystals are secured. l

The switching arrangement 8 provides means for effectively utilizing any crystal in the container 1. Connected to the switch arm 8 and also to the lower contact plate 3 are the binding posts 31 and 24, respectively from which leads may be taken to a desired control circuit. The crystals 20, 21 and 22 may have different fundamental frequencies and by moving switch 8 to the different contacts 5, 6 or 7, the desired frequency control may be selected.

In order to maintain the crystals at a desired temperature or range of temperatures within the container, I provide a heating coil 28which. is mounted interiorly of the containerwl and connected to binding posts 26 and 27 with the source of energy 25 and through the therlnostatic regulator 29 and 30. rI`he thermostatic regulatorf29 and 30 functions to make contact at temperatures below a certain value and break contact at temperatures above this value. By this arrangement'the local source vof energy 25 may be connected or disconnected from the heating coil 28 in order to maintain proper temperature condition within the container.

The container 1 is hermetically sealed in such manner that moisture and foreign matter is excluded and prevented from creeping into the container. This arrangement is 'particularly desirable where the piezo electric crystal system is used in electron tube trans- .mitters which are Subj ect to exposure on shipboard and in aircraft and where the frequency constant. The mountings for the crystals are such that each crystal is free to oscillate in its own natural period and under conditions of a given temperature range independent of changes in humidity. Y

While I have described my invention in a certain particular embodiment, I desire that it be understood that modifications may be made and that I intend no limitations upon the invention other than those imposed by the scope of the appended claims.

What I claim and desire tosecure by Letters Patent of the United States is as follows:

1. Piezo electric quartz crystal apparatus comprising Ain combination a plurality of piezo electric quartz.crystalseacl1 capable of cies, a container for said quartz crystals hermetically sealed against the atmosphere. an electric heating device within said container adjacent said quartz crystals for maintaining being set into oscillation at different frequenlll said quartz crystals at a given operating temperature, and switching means for selecting anyone of said quartz crystals for operation -selected frequencies means for establishing electrical connections with opposite faces of said crystals, means within said container for maintaining said quartz crystals at aselected temperature and means for rendering said crystals individually edective to sustain oscillations. 3. Piezo electric quartzcrystal apparatu comprising in combination a container, a metallic base within said container, a plurality of upstanding peg members in said base, a plurality of quartz crystals each capable of being set into oscillation mounted between said peg members, a plurality of contact plates each resting upon said quartz crystals, spring means within said container bearing upon each of said Contact plates for establishing 'electrical connections with the upper faces of said quartz crystals, and means within said container for maintaining said quartz crystals at a desired temperature, whereby variations of humidity conditions are prevented from iniuencing the characteristic properties of said crystals.

a. A. piezo electric quartz crystal system comprising in combination a quartz crystal container, a metallic base member within said container, a plurality ci crystal retaining means carried byY said base member, a plurality of quartz crystals each capable of being set into oscillation secured within said crystal retaining means, metallic contact plates bearing upon the upper surfaces of said quartz crystals for Shing electrical connection therewith, swi c ing means for electrically selecting an individual one of said crystals for the sustaining ot oscillations at a frequency corresponding to a selected crystal and means within said container whereby variations ot temperature and humidity conditions are prevented from influencing the characteristic properties of said crystals.

5. In a piezo electric crystal apparatus, the,1

combination with a plurality of piezo electric crystals each capable or' being set into oscillation, of a plurality ol list metallic plate members each arranged to contact with the upper surfaces of said piezo electric crystais, a. single flat metallic plate member arranged to contact with each of the lower surtaces oi' said crystals, and a plurality of tongues extending from each of said plates toward each other for locating said crystals within limits between said plates.

6. Piezo electric crystal apparatus comprising in combination a dat metallic supporting' member, a piezo electric crystal mounted on said supporting member, a conductive plate having its surface contacting with the upper surface of said piezo electric crystal members extending upwardly from said supporting member and downwardly from said conductive plate for embracing the edges of said crystal, and means for establishing a selected pressure on said plate for improvingthev operating characteristics of said crystal.

t?. Piezo electric crystal apparatus comprising in combination a dat metallic supporting member, a piezo electric crystal mounted on said supporting member, a conductive plate having its surface contacting with the upper surface of said piezo electric crystal means projecting alternately from said suporting member and from said plate and directed toward each other for confining said crystal in a selected position, and a spring device engaging said plate for subjecting said piezo electric crystal to a predetermined selected pressure for improving the operating characteristics of said crystal.

8. Piezo electric crystal apparatus comprising in combination a flat metallic supporting member, a piezo electric crystal mounted on said supporting member, a conductive plate having its surface contacting with the upper surface of said piezo electric crystal conductive members protruding from Asaid supporting member and from said plate and embracing the edges of said crystal for locating said crystal in a predetermined position vand a flat metallic spring strip'extending over said piezo electric crystal with the end thereof in 'engagement with said conductive plate for subjecting said piezo electric crystal to pressure for improving the operating characteristics thereof.

9. Piezo electric crystal apparatus/comprising in combination a fiat metallic supporting member, a piezo electric crystalv mounted on said supporting member, a conductive plate having its surface contacting with the upper surface of said piezo electric crystal means carried by said plate and by said supporting member for locating said piezo electric crystal therebetween and a spring strip iXedly positioned at a point adjacent one side of said piezo electric crystal and extending over said crystal and establisliing electrical contact vwith said plate while exerting a predetermined pressure on said crystal for improving the operating characteristics thereof.

10. Piezo electric crystal apparatus coinprising in combination a tlat metallic supporting member, a piezo electric crystal mounted on said supporting member, a conductive plate having its surface contacting lill with the upper surface of said piezo electric crystal means extending from said supporting member and said conductive plate for embracing the edges of said piezo electric crystal and confinin the piezo electric crystal in a lateral plane etvveen said supporting member andI said plate, and means for loading said piezo electric crystal under a selected Weight for improving the operating characteristics thereof.

11.l In a frequency control system, a cabinet, a selector switch having a multiple number ot positions and operative from the en terioi' of said cabinet, a multiplicity ot' piezo electric crystal units ot differing frequency characteristics mounted within said cabinet and individually connected to said selector switch for connection in a frequency control circuit in accordance with changes in position of said selector switch, and means in said cabinet 'for maintaining said piezo electric crystalunits under predetermined temperature and humidity conditions for sustaining constant frequency oscillations independent of changes in temperature and humidity conditions external to said cabinet.

12. In a device for sustaining constant freguency oscillations in an electron tube high rcquency generator the combination of a piezo-electric quartz crystal capable ot beiny set into oscillation, a housing enclosing sai crystal and means Within said housing for maintaining said crystal at a predetermined Lampes plurality of piezo-electric crystals mounted for free vibration within said container, ya plurality of electrodes electrically associated with said crystals, a switching device connected to said electrodes, means exterior to said container for selectively actuating said 'switching device to establish connections with selected electrodes, and means for maintaining a predetermined temperature Within said container.

16. 'lihe method of maintaining constant the operating frequency of a piezo-electric quartz crystal enciosed Within a container which is hermetically sealed, which consists in supplying heat to said container and regulatingthe supply et heat thereto so that said crystal is maintained at asubstantially constant temperature sudiciently high to prevent condensation of moisture on the surface oli' said crystal.

17. 'lhe method of maintaining constant the operating frequency of a iezo-electric quartz crystal, `a'lriich consists in operating said cr stal in a confined atmosphere, supplying eat to said confined atmosphere, and regulating the supply of heat so that said crystal is maintained at a substantially constant temperature sulhciently high to prevent condensation or moisture on the surface of said crystal. I

: ALFRED CROSSLEY.

temperature suiiciently high to prevent the r condensation of Water vapory upon the surfaces of said crystal.

' 13. In a device for sustaining constant frequency oscillations in an electron to high frequency generator, the combination of a piezo electric quartz crystal capable of being set into oscillation, a hermetically sealed housing for said uartz crystal and means Within said housing or heating the interior thereof over.`

a given range of temperature for maintaining said quartz crystal at a selected temperature sufficiently high to prevent the condensation of water vapor upon the surfaces of said crystal.

14. In a piezo-electric crystal apparatus the combination of a container sealed to pre-` vent free passage of atmosphere, a piezo-electric device mounted for free vibration within said container, a lurality of electrodes velecl/trically associate with said piezo-electric device and having connections extending ex- Y terior to said container, means for holdin said piezo-electric device in a predetermine position with respect to said electrodes and means for maintaining a predetermined temperature of the atmosphere within said oontainer suiliciently high to prevent the conden.-

sation of water vapor upon the surfaces of.

said crystal. p

15. In a piezo-electric crystal apparatus tlieeombination of a dustproof container, a

'StammA Noi. 1,901,735.

A (Seel) CERTIFICATE 0F coR'Re-EGTIGN. y

I u' 'March 14,1933.

,1 cRossLEY. A V it is hereby certified that'error appears in the'printed specification of the Aamve. numbered patent requiritig correction as follows Page 4, line 38, claim 13, for "to" read "tube"; andihat the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the` Patent Office.V v A Siwed and`sealed this 18thl day of April. A. D, H933.

MJ. Mmm-j Aetim Commissioner of Patents. 

